1. Field of the Invention:
The present invention relates to an ink-jet recording ink having good light-fastness, good color reproducibility and high reliability and capable of giving high-quality images, to an ink-jet recording color ink set including the ink, and to an ink-jet recording method using the ink set.
2. Description of the Related Art:
The principle of ink-jet recording systems is that liquid or melted solid ink is jetted out through nozzles, slits, porous films or the like onto recording media such as paper, cloth, film and the like to thereby record images and others on the media. For jetting out ink, various systems have been proposed, including, for example, a charge control system where ink is jetted out by electrostatic induction force; a drop-on-demand system (pressure pulse system) where ink is jetted out by the oscillation pressure of piezoelectric devices; a thermal ink-jetting system where ink is jetted out by the pressure of bubbles formed and grown under heat at high temperatures, etc. In these systems, formed are extremely fine images.
Various types of ink are known usable in these ink-jet recording systems, including, for example, aqueous dye ink to be prepared by dissolving a water-soluble dye in a liquid medium that contains water and a water-soluble organic solvent; aqueous pigment ink to be prepared by dispersing a pigment in a liquid medium that contains water and a water-soluble organic solvent; oily dye ink to be prepared by dissolving an oil-soluble dye in an organic solvent, etc.
Of those types of ink, aqueous ink that contains a water-soluble dye dissolved in water is the mainstream of ink-jet recording ink. This is because it is safe as the essential solvent for it is water, and, in addition, it gives good and high-quality color images as it contains a dye, and further, it has good storage stability.
On the other hand, the recent demand in the art of ink-jet printing is for forming high-quality print images nearer to photographic images. For forming color images, it is important that magenta ink, cyan ink and yellow ink all have good color reproducibility by themselves, additionally having good color reproducibility to give secondary colors, red (R), green (G) and blue (B) when they are printed in layers. In order to obtain high-quality print images nearer to photographic images, plural inks having different color density levels are printed in layers. In consideration of this, it is also important that the plural inks do neither bleed nor mix together when printed plural times in layers, and, in addition, the printed inks could dry as soon as possible without delay. On the other hand, the resolution of print images is desired to increase in a high-resolution, small-drop ink-jet recording method. For this, the diameter of the nozzle of the ink-jet recording head to be used in the method is reduced, and it is important to prevent the nozzle from being clogged. In order to stably store print images for a long period of time without deteriorating their quality, it is important that the printing ink to be used for forming them has good fastness including waterproofness, light-fastness, etc. However, of four color inks of magenta, cyan, yellow and black for forming full-color images, magenta ink is readily deteriorated by light, and, as a result, the quality of images containing it is often much deteriorated.
To improve the light-fastness of such aqueous magenta dye ink, various studies and developments have been made. For example, in Japanese Patent Publication No. S61-57878, proposed is a method of adding a dye having a specific structure to ink to thereby improve the light-fastness of the ink. The ink containing such a specific dye could have good light-fastness, but is still problematic in that the images formed of it often bleed and it often clogs nozzles of small-drop heads.
In Japanese Patent Laid-Open Nos. H06-100790, H07-166084 and H09-255887, proposed are novel dyes having a specific absorbance profile. These dyes have good color reproducibility, but are also problematic in that their light-fastness is poor. In particular, when they are used in color ink sets for forming color images, expression of magenta-containing secondary colors of read and blue is poor.
On the other hand, for overcoming the problem with the color printing technology as above, proposed is a method of using C.I. Direct Red 227 as the colorant for magenta ink to thereby improve the color reproducibility of the ink, as in Japanese Patent Laid-Open No. H09-3380. In this method, however, the light-fastness of the magenta ink used is not good, and the storage stability of the color print images produced is not satisfactory.
As mentioned above, at present, no one could obtain satisfactory ink-jet recording ink, especially water-soluble ink for ink-jet recording which satisfies all the necessary properties including good light-fastness, good color reproducibility, especially good color reproducibility of magenta-related secondary colors of red and blue, and high reliability, and which gives satisfactory high-quality images.
Solving the problems in the related art as above, the present invention provides excellent magenta ink for ink-jet recording. Specifically, the magenta ink of the invention satisfies all the necessary properties including good light-fastness, good color reproducibility, especially good color reproducibility of magenta-related secondary colors of red and blue, and high reliability, and gives satisfactory high-quality images. The invention also provides a color ink set for ink-jet recording, which contains the magenta ink; and an ink-jet recording method in which is used the magenta ink or the color ink set.
Having assiduously studied, the present inventors have found that magenta ink, which comprising a water, a colorant and at least two water-soluble organic solvents, and of which the visible-light absorbance spectrum gives a first peak A (abs.) within a range of from 500 to 570 nm and a second peak B (abs.) within a range of from 300 to 350 nm with a ratio A/B falling between 0.9 and 2.5, is favorable to ink-jet recording, as having good light-fastness, good color reproducibility and good printing frequency responsibility and capable of forming excellent high-quality images without clogging nozzles. On the basis of this finding, we have completed the present invention.
Specifically, the invention provides:
Magenta ink for ink-jet recording, which comprisig a water, a colorant and at least two water-soluble organic solvents and of which the visible-light absorbance spectrum gives a first peak A (abs.) within the range of approximately from 500 to 570 nm and a second peak B (abs.) within a range of approximately from 300 to 350 nm with a ratio A/B falling approximately between 0.9 and 2.5;
The magenta ink for ink-jet recording, wherein the water-soluble organic solvents are at least two selected from polyalcohols, polyalkylene glycols, glycol ethers and polar solvents;
The magenta ink for ink-jet recording, wherein the content of the water-soluble organic solvents is approximately from 3 to 40% by weight of the ink;
The magenta ink for ink-jet recording, wherein the colorant is an anionic water-soluble dye and its content is approximately from 0.1 to 10.0% by weight of the ink;
The magenta ink for ink-jet recording, which contains (i) at least one surfactant selected from nonionic, anionic and ampholytic surfactants in an amount of approximately from 0.005 to 5% by weight of the ink, and (ii) a nitrogen-containing compound having a carboxylic acid and/or sulfonic acid structure, of which the pKa at 20xc2x0 C. falls approximately between 6.0 and 10.0, and (iii) an alkali metal hydroxide;
The magenta ink for ink-jet recording, of which the pH falls approximately between 5.0 and 12.0, the surface tension, xcex3, falls approximately between 20 and 45 mN/m, and the viscosity, xcex7, falls approximately between 1.5 and 5.0 mPas;
A color ink set of magenta ink, cyan ink and yellow ink for ink-jet recording, which contains water, colorants and at least two water-soluble organic solvents and contains the magenta ink mentioned above;
The color ink set for ink-jet recording, wherein the colorant for the cyan ink is at least one selected from C.I. Direct Blue 86, C.I. Direct Blue 199, C.I. Direct Blue 307 and C.I. Acid Blue 9, and the colorant for the yellow ink is at least one selected from C.I. Direct Yellow 86, C.I. Direct Yellow 132, C.I. Direct Yellow 142, C.I. Direct Yellow 144 and C.I. Direct Yellow 173;
The color ink set for ink-jet recording, wherein the cyan ink and the magenta ink both have at least two colorant density levels;
An ink-jet recording method, wherein the magenta ink or the color ink set as above is used and the amount of one ink drop to be jetted out through a nozzle falls approximately between 1 and 20 ng; and
The ink-jet recording method, which is to print an image on an ink-jet recording sheet having at least approximately 40% of 75-degree mirror surface gloss as defined in JIS-Z-8741.